The present invention relates to a very low cost portable compact scanner employing a single scanning carriage incorporating a reading head and optionally a printing head to permit the reading of an original document or when the scanning carriage has both a reading head and a printing head it can provide essentially simultaneous reading and writing of an original document and a copy. More particularly, it is directed to a floating document backstop to precisely locate a document on the imaging platen during an imaging operation.
Historically, copies of original documents have been produced by a xerographic process wherein the original document to be copied is placed on a transparent platen, either by hand or automatically through the use of a document handler, and the original document illuminated by a relatively high intensity light. Image rays reflected from the illuminated document are focused by a suitable optical system onto a previously charged photoconductor, the image light rays functioning to discharge the photoconductor in accordance with the image content of the original to produce an electrostatic latent image of the original on the photoconductor. The electrostatic latent image so produced is thereafter developed by a suitable developer material commonly referred to as toner, and the developed image transferred to a sheet of copy paper brought forward by a suitable feeder. The transferred image is thereafter fixed to the copy paper by fusing to provide a permanent copy while the photoconductor is cleaned of residual developer preparatory to recharging. More recently, interest has arisen in electronic imaging where, in contrast to the aforedescribed xerographic system, the image of the document original is converted to electrical signals or pixels and these signals, which may be processed, transmitted over long distances, and/or stored, are used to produce one or more copies. In such an electronic imaging system, rather than focusing the light image onto a photoreceptor for purposes of discharging a charged surface prior to xerographic development, the optical system focuses the image rays reflected from the document original onto the image reading array which serves to convert the image rays to electrical signals. These signals are used to create an image by some means such as operating a laser beam to discharge a xerographic photoreceptor, or by operating some direct making system such as an ink jet or thermal transfer printing system.
It is generally advantageous if the normally separate document reading and copy printing operations could be combined. If some of these reading/writing functions could be combined, system operation and synchronization could be simplified and system cost reduced through the use of fewer parts.
In the above cross-referenced previously filed applications, an input output scanner concept is described wherein a single pair of paper path rolls drive both the document at the 12 o'clock position and the copy paper at the 6 o'clock position and the circumference of each roll is equal to the width of the reading head and the writing head. The scanning carriage has secured thereto a reading head and a printing head which carriage system scans across a document scanning a band of information across the document and prints a band of information across a copy sheet. The carriage system has a separate indexing mechanism to index the document and copy sheet to a second position to scan another band of information across the document. Between imaging scans both the paper and the document are advanced exactly the same amount by one complete revolution of the drive rolls thus eliminating the need for tight control of the run out tolerances on the rolls thereby insuring lower costs for the parts.
Most copiers, printers, facsimile machines and scanner devices use multiple electromechanical actuators such as motors, clutches, solenoids, etc. to operate the various components of the machine at various times in the processing cycle. Even in the compact combined input/output scanner described in the above cross-referenced previously filed applications, there were two motors required. One was used to move the scanning carriage and the second was used to advance both the document and the copy paper. For each electromechanical actuator, there are costs which must be born besides the unit cost of the actuator itself. These include a power supply to drive the device, harness costs to carry the power and control signals to the device, assembly costs to install the device, the power supply and the harness and electronic circuitry to control the devices and often some kind of voltage control circuitry to ensure proper operation of the devices over a wide range of operating voltages.
In addition, in the above-referenced previously filed application the circumference of the index drive roll is equal to 384 pixels at 16 per millimeter which means its diameter is about 7.7 millimeters which means that the optical system must fit within the 7.7 millimeters height constraint. The present invention is directed to meeting this architectural constraint with the minimum number of parts at the lowest cost.